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[18.04] Long-Term Variations of Jupiter's Mid-to-Low Latitude H₃⁺ Emission Observed at IRTF

T. Satoh (Kumamoto University), J. E. P. Connerney (NASA GSFC)

Jupiter's diffuse H₃⁺ emissions covering the mid-to-low latitude resion were detected by spectroscopic observations (Ballester et al., Icarus 107, 189, 1994; Marten et al., Planet. Space Sci. 42, 391, 1994). Miller and colleagues (Icarus 130, 57, 1997) studied its spatial variations by combining a series of slit spectra taken along the central meridian with various rotation phases. The ionospheric H₃⁺ ion is a key element to the thermal balance in Jupiter's upper atmosphere.

Satoh and Connerney (GRL 26, 1789, 1999) demonstrated the usefulness of imaging observations of Jupiter's mid-to-low latitude H₃⁺ emissions. Their conclusions include: (1) the apparent limb brightening is consistent with the line-of-sight effect, evidencing that the layer of H3+ emission is indeed optically thin, and (2) the true disk emission (corrected for the line-of-sight effect) can be well reproduced with H₃⁺ peak density 9.6 \times 10³ cm^-3 at an altitude 700-750 km (7-5 nb pressure) above P = 600 mb level. The imaging observation of Jupiter's mid-to-low latitude H₃⁺ emission is thus useful to study the vertical distribution of this ion, especially if the data are compared with sophisticated atmospheric models such as JIM (Achilleos et al., JGR 103, 20089, 1998).

To extend the previous studies, we have analyzed more H₃⁺ images including: (1) those acquired using the ProtoCAM (1992-93 observations), (2) those acquired using the NSFCAM plus the IRTF standard circular-variable filters (CVF; 1995-98 observations), and (3) images of the highest signal-to-noise and the spatial resolution acquired using the NSFCAM plus a special H₃⁺ filter (1999-2000 observations). These images have been cross-calibrated by measuring the flux of several standard stars as well as that of Jupiter's Galilean satellites. We have found that the mid-to-low latitude emissions were very stable throughout years of observations, and that there are several bright/dark patches in higher latitudes (but equatorward of the intense aurorae), which seem to be related to the surface magnetic field strengths. Details of these data and implications to the studies of Jupiter's upper atmosphere will be discussed.

The author(s) of this abstract have provided an email address for comments about the abstract: tsatoh@educ.kumamoto-u.ac.jp

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